Eric Broens writes:
Thank you for your reply. I have finally found what caused the problem after encountering the "HTTP Error 409: Subscription request already pending". Thanks to the archives of the mailman-users mailing list, I found out that there was a long list of pending confirmations for the slow mailinglists, mostly from non-real subscribers.
Glad you found the issue.
I haven't seen this myself yet, but apparently there's a malicious campaign going on where mass subscription attempts are conducted via TOR (if you're not familiar with TOR, it's a way to obfuscate the source and target addressas of a connection). One person reports a subtantial reduction in such malicious subscriptions:
https://lists.mailman3.org/archives/list/mailman-users@mailman3.org/thread/B...
Steve